Attention deficit hyperactivity disorder (ADHD) has an estimated incidence in school age children of 3-5%, and is characterized by the core symptoms of hyperactivity, impulsivity, and/or inattention. The attentional symptoms of ADHD can be successfully treated with psychomotor stimulants such as methylphenidate (Ritalin). Clonidine, an α2-adrenoceptor agonist, treats the aggressive and oppositional symptoms. There is a potential for significant side effects with both methylphenidate and clonidine, making it important to identify other drugs that have similar or better efficacy with reduced side effects and abuse liability.
ADHD is one of the most common childhood psychiatric disorders and appears to be a common, often under recognized, psychiatric disease in adults as well (T. Spencer, et al., J Clin Psychiatry, 1998, 59 (Suppl. 7), 759-768). This disorder, which begins in childhood, may be followed by a lifelong expression of symptoms (e.g., inattention and/or impulsivity) (J B. Schweitzer, et al., Med Clin North Am, May 2001, 85:3, 757-777). ADHD may change its manifestations as it develops from preschool through adult life (D P. Cantwell, J Am Acad Child Adolesc Psychiatry, August 1996, 35 (8), 978-987; J. Elia, et al. N Eng J Med, March 1999, 340 (10), 780-788; E E. Nolan, et al., J Am Acad Child Adolesc Psychaitry, February 2001, 40 (2), 241-249).
The diagnosis of ADHD is based on clinical evaluation (M. Dulcan, et al. M, J Am Acad Child Adolesc Psychaitry, October 1997, 36 (10 Suppl), 85S-121S; National Institutes of Health, 1998). “The essential feature of ADHD is a persistent pattern of inattention and/or hyperactivity-impulsivity that is more frequent and severe than is typically observed in individuals at a comparative level of development” (Diagnostic and Statistical Manual of Mental Disorders (DSM-IV), American Psychiatric Association, Washington, D.C., 1994). In order to be diagnosed with ADHD, patients must demonstrate symptoms of ADHD that cause impairment before the age of seven years, and symptoms must have been ongoing for longer than six months in at least two settings (e.g., school [or work] and home). (See DSM-IV).
Several NRI compounds are known. Atomoxetine, an NRI, is now commercially available (Strattera®, Eli Lilly) and is beginning to be used extensively for the clinical treatment of ADHD in both children and adults. Atomoxetine represents a non-stimulant treatment for ADHD. The number of treated ADHD patients is expected to increase as a result of the introduction of atomoxetine and enhanced educational initiatives. Accordingly, there is an ongoing need for ADHD treatments that provide more efficacy than those treatments currently available.